Macroautophagy, herein referred to as autophagy, is a highly conserved process for cellular degradation and recycling of cytosolic contents to maintain cellular homeostasis. Autophagy substrates are generally cellular organelles, long-lived proteins and aggregate-prone proteins. Due to its functionality to clear cytosolic contents, this highly conserved process has been shown to be a promising approach for treatment of diseases characterized by the formation of intracellular aggregates, such as aging of the brain and neurodegeneration. Dysfunction of the autophagy pathway has also been implicated in various cancers.
Aggregate-prone disorders are characterized by the formation of intracellular aggregates in specific tissues. For example: neurodegenerative diseases are associated with the accumulation of abnormal protein aggregates in affected regions of the brain. One example of a disease-causing, aggregate-prone protein is alpha-synuclein (α-syn). Over-expression of α-syn due to duplication or triplication of the α-syn gene locus has been shown to result in familial form of Parkinson's disease (PD). Point mutations (A53T and A30P) of α-syn increase the aggregation propensity thereof also lead to early onset of familial PD. Moreover, over-expressions of wild type (WT) and mutant α-syn in transgenic mice as well as transgenic flies have been found to cause progressive locomotor defects with dopaminergic neuron loss and intracytoplasmic inclusions. It is also believed that accumulation of α-syn oligomers, which are intermediates of fibrillar aggregates or inclusion formation are toxic and lead to direct neuronal death. These findings illustrate that α-syn as valuable therapeutic target for the treatment of PD and other synucleinopathies.
Other examples of aggregate-prone disorders include Alzheimer's disease; Hungtinton's disease; spinocerebellar ataxia types 1, 2, 3, 6, 7 and 17; spinobullar muscular atrophy; dentatorubral-palli-doluysian atrophy; different forms of dementia that are caused by mutations in the neuronal protein tau; forms of motor neuron disease caused by mutations in superoxide dismutase 1 (SOD1) and forms of peripheral neuropathy caused by mutations in peripheral myelin protein 22 (PMP22).
Apart from α-syn, it is well-established that other large disease-causing protein aggregates like oliogomeric α-syn, tau and mutant huntingtin, are also relied greatly on autophagy pathway for clearance since they cannot go through the narrow core of proteasomes for degradation. Furthermore, recent reports using mutant mice lacking the autophagy-related genes atg5 or atg7 indicate basal autophagy has an important role in neuronal functions.
Certain bacterial and viral infections may also be treatable by autophagy upregulation, since the pathogens can be engulfed by autophagosomes and transferred to lysosomes for degradation. For instance: Mycobacterium tuberculosis; Group A Streptococcus and Herpes Simplex Virus Type I.
Approaches to activate autophagy for therapeutic applications, such as treating neurodegenerative diseases and cancers have been explored in the art. For instance: Bradner et al. (WO2008/122038) discloses various modulators of autophagy such as compounds with a bis-indolyl maleimide core for the treatment or prevention of neurodegenerative diseases, proliferative diseases as well as infectious diseases; Rubinsztein et al. (US20070155771) describes the use of rapamycin for the treatment of conditions characterized by formation of intracellular protein aggregates by stimulation of autophagic activity and Yuan et al. (US2010/0267704) discloses treatments using autophagy inducing compounds including Loperamide, Amiodarone, Niguldipine, Pimozide.
However, current small molecules which upregulate autophagy in mammalian brains such as rapamycin, are specific mTOR inhibitors. TOR proteins are known to control several cellular processes besides autophagy in organisms from yeast to human. Thus, long-term use of these mTOR dependent small molecule autophagy inducers is likely to contribute to complications. Moreover, autophagy in the central nervous system is also known to be regulated differently from that in non-neuronal cells and the induction thereof in neuronal cells has been shown to be more difficult than in non-neuronal cells. These classical autophagy inducers either fail to induce autophagy in the cortex of mouse brains or induce only mild autophagy in neurons.
Corynoxine B (Cory B), one of the Uncaria oxindole alkaloids has been used as a component of various compositions to induce various biological outcomes, such as protective effects on ischemia-induced neuronal damage; inhibition of Listeriolysin O-induced nitric oxide and endothelin-1 release and prevention angiotensin II induced proliferation. Nevertheless, there is no teaching or suggestion in the prior art relating to this kind of compounds (oxindole alkaloids) to induce autophagy.
Accordingly, there is a need for a potent agent which specifically induces autophagy independent of mTOR in neurons for the treatment of diseases that can benefit from autophagy, including but not limited to neurodegenerative disorders, immunological diseases, cardiac diseases and cancer.